/Engine/Source/Runtime/Engine/Classes/Materials/MaterialInterface.h
Return the textures used to render this material and the material indices bound to each. Because material indices can change for each shader, this is limited to a single platform and quality level. An empty array in OutIndices means the index is undefined.
virtual void GetUsedTexturesAndIndices ( [TArray](API\Runtime\Core\Containers\TArray)< [UTexture](API\Runtime\Engine\Engine\UTexture) * > & OutTextures, [TArray](API\Runtime\Core\Containers\TArray)< [TArray](API\Runtime\Core\Containers\TArray)< int32 > > & OutIndices, [EMaterialQualityLevel::Type](API\Runtime\Engine\EMaterialQualityLevel__Type) QualityLevel, [ERHIFeatureLevel::Type](API\Runtime\RHI\ERHIFeatureLevel__Type) FeatureLevel ) const